Sandra from Perth, Australia, is Skyping™ in during the wee hours of the morning to ask about something she hopes will be the answer to her dieting prayers. "I actually saw some headlines recently that actually said that there's an exercise pill, and it's a dream come true," she says. "Is there an exercise pill that can be healthy and you still don't have to exercise?"

Dr. Oz says there is some truth to this couch potato's fantasy. There is a pill—but it's only in "rat stage." "If there's an exercise pill, I would have had it, and then it would have become one of my favorite things, and I would have told you all about it," Oprah says.

Dr. Oz says scientist Ronald Evans has been researching the differences between the best athletes around and people who have trouble losing weight. It all comes down to cells called mitochondria—the "energy factories" found in each muscle cell. Athletes have a lot of mitochondria and get more out of their exercise—people who tend to gain a lot of weight don't have as many.

Dr. Oz says the weight loss pill has been tested on rats, and the ones who got the pill ran almost 50 percent further than those who didn't. The rats who got the pill and some training were able to go 75 percent more than any other rat.

Dr. Oz says he thinks a weight loss pill for humans could be a possibility someday, but he emphasizes the importance of working out for yourself. "If you can exercise, it is a much better way of getting the results we want," he says. "When you exercise, you're getting a double dividend. You're getting the benefit of losing the calories while you exercise, plus you're training your body to burn more calories even when you're not exercising."